To operate our airplane as efficiently as possible, when we get it done with it that is, it is going have to be operated at high altitudes. It's simply easier to propel it through the thinner air at high altitude than through the dense air down low.

To make our airplane fly we must understand something of the applied science that provides the principles that allow machines to fly through the air - aerodynamics. Whoops, there's that first huge intimidating word. Don't quit yet though, it's not going to be as bad as you might think.

We live on the surface of the earth which is actually an ocean floor. That's right we live on the bottom of an ocean of air. That, of course, means that the air, although invisible, IS something. Therefore, it weighs something. (The weight of a column of air one inch square and the height of the atmosphere weighs approximately 15 pounds at sea level.) And because air is something we can use the air to our advantage in much the same way that we use water to our advantage when we swim. As they say in a recent Infinity car ad on television, "You can either fight the wind, or make it your friend." In fact, even though air is a mixture of gases, it acts more like a fluid.

Leave your computer now and take some time to think about this ocean of air analogy and go out and perform a simple experiment: Get into your car in the front passenger seat. Let someone else drive. Extend your arm out the open window on your side of the car. Nothing feels different before the car starts to move because like always the weight of the air is exerting a pressure over the entire surface of your hand and arm equally.

Have "your driver" drive the car at 20 miles per hour, again extend your arm out the window only this time turn the palm of your hand forward, fingers together. You now feel a force on the palm of your hand;The faster the car goes the greater the pressure. The force you feel is produced by the palm of your hand impacting millions of air molecules as it is propelled forward by the car. This force is called DRAG. (whoopee, your first aerodynamic term.)

Now, as the car proceeds at a constant 20 miles per hour turn your hand 90 degrees so that the palm is down. Your hand is now a "wing". Notice that the force you now feel depends the angle your hand is to the oncoming air. This angle is called the ANGLE OF ATTACK, because this is the angle at which the surface of your hand attacks the air. If the angle is exactly into the oncoming air, or at a zero ANGLE OF ATTACK, the only force you feel is a slight drag force on the leading edge of your hand along your index finger. However, if you increase the angle of attack, by turning your hand slightly clockwise, you will start to feel a strong force trying to pull your hand and arm up. This force is a combination of low pressure on top of your hand pulling it up, and a higher pressure on the palm of your hand pushing it up. Your hand is now producing LIFT. If your hand had more curvature (CAMBER) on the upper surface than on the lower surface then even more lift would be produced.

There are several things you should take away from this experiment:The amount of lift produced is a function of the area of your hand, the "wing" if you will, the ANGLE OF ATTACK of your hand, and the amount of curvature of your hand.

One other factor, which you have probably already guessed, that effects the amount of lift produced by a given wing is the air density. The denser the air the more lift is produced.

The last thing is that no lift is produced by the wing unless it is moving through the air. Lift (or drag) is a force produced by the reaction of the air to the wing moving through it. This should provide much solace to air travelers because as long as the airplane, in which you may be riding, is moving through the air at sufficient speed to produce the minimum amount of lift it will stay in the air!

To apply this learning to our "airplane" we need to build two wings, one will be attached to the fuselage extending to the left, the other the same but opposite, will be attached to the fuselage and extending to the right. Left and right as we face forward in the fuselage. Both wings will be attached to the fuselage at a slightly positive ANGLE OF ATTACK so that positive lift is produced at all times (this angle is called the ANGLE OF INCIDENCE, what ever that is worth).

The wings will be rounded on the front edge (the LEADING EDGE), and "sharp" along the back or TRAILING EDGE. They will have more curvature on the top surface than on the bottom surface to produce as much lift as possible for their size. Most of time the wing's of an airplane are tapered in two directions;as they are viewed from the top, and as viewed from the front. This is done to increase lift production, decrease drag, and for increased structural efficiency. The airplane just needs less wing the further out from the sides of the fuselage you go.

The wings on virtually all jet passenger planes are swept back. This decreases drag by making the wing appear, to the air passing over it, to be thinner than it actually is. How big do we make them? Well, each square foot of area of a wing with a given cross-section will produce a certain amount of lift. In flight, lift from the wing is an upward force applied to the entire airplane. In order for the airplane to maintain a given height above the surface of the earth this lifting force must equal the weight of the airplane. So, the wing must have at least enough square feet to support the airplane at its maximum weight at the maximum altitude at which it is designed to fly.

The exact size and shape of the wing is carefully and painstakingly developed for each particular airplane in all phases of flight for maximum aerodynamic and structural efficiency, in a wind tunnel. A wind tunnel is a very sophisticated equivalent of the experiment you previously performed by sticking your hand out of the window a moving car.

In a wind tunnel various models of a proposed wing are placed in a closed tube. (Models are used because there are no wind tunnels large enough to accept a full sized airplane;imagine how large the tunnel would have to be to accept a fullsize Boeing 747.) A fan blows air of varied density through the tunnel past the wing model at speeds equivilent to the speeds at which the airplane is expected to fly and the forces of lift and drag thus produced by the model wing are carefully measured. Various models of different sizes and shapes are tested until the the desired degree of efficiency is achieved, and only then is the actual full size wing designed for the airplane.

It is interesting to note that the Boeing Company is the world leader in building the most efficient airliners because the company maintains it's own wind tunnel. This has allowed them to spend more time fine tuning not only the wings used on their airplanes, but fine tuning the entire airplane for maximum efficiency, as well. Most other companies did not have this luxury. They had to rent wind tunnel time from someone else.

In addition to providing lift the wings serve at least three other purposes:

(1) The wings are used for control of the airplane. At the tips of each wing, mounted on the trailing edge, are small moveable sections called AILERONS (small relative to the size of the size of the wing that is). These surfaces move differentially; as the left one moves trailing edge up, the right one moves trailing edge down. This causes the airplane to rotate counterclockwise about the centerline of the fuselage. The centerline of the fuselage is called the LONGITUDINAL axis, and the aircraft's rotation about this axis is ROLL. This is how the airplane is turned. The ailerons are moved by turning the pilots control wheel.

(2) The wings are used for lift control. Hinged to the trailing edge of the wing between the ailerons and the fuselage are movable surfaces called flaps. Flaps are lift increasing devices. As the airplane slows down, to land let's say, lift is decreased. Remember that if the wing is setting still NO lift is produced; so the slower the airplane flies the closer it gets to not moving at all and the less lift is produced. At the slower speeds there are two things we can do to maintain the required lift. We can increase the angle of attack, or increase the curvature (CAMBER) of the wing.

We are limited in the amount we can increase the angle of attack. Remember riding along with your hand perpendicular to the airflow? All you felt was drag and the angle attack was 90 degrees. No lift was being produced. Somewhere between zero and 90 degrees angle of attack all lift is lost and the airplane is said to stall. The stall angle for most wings is between 15 and 18 degrees angle-of-attack.

In addition, as the airplane flies at a higher angle it becomes more difficult for the pilot to see the runway over the nose, and it becomes more difficult to land. The British made Concorde, because of the specially shaped wing it must have to go very fast, must also land at a very high angle. The pilot can only maintain an adequate view of the runway during the landing phase of flight only if the nose of the airplane is "drooped" out of the way.

The flaps unlike the ailerons move together. As the speed get slower and slower the flaps are lowered which increases the curvature of the upper wing surface. As you learned earlier a wing with more curvature on the upper surface produces more lift.

(3) The wings are used to store fuel. During manufacture the mating surfaces of the various parts that make up the wing are coated with a sealent. This special sealent is impervious to chemicals like jet fuel. Once the parts are fastened together and the sealent cures the wing structure becomes a sealed container. This huge container on an airplane the size of our airliner can store thousands of gallons of fuel. This fuel in an airplane the size of the one we are building provides for thousands of miles of range.

So, we have come a long way! Our airplane has a fuselage in which we can carry a little over 200 passengers, and a wing to provide the appropriate amount of lift force under all operating conditions.

Next time we will install some engines to provide the power to make all of this work, and some additional aerodynamic surfaces on the rear of the fuslage to provide additional required stability and control.